Helical pitch in mixtures of cholesteric liquid crystals

Abstract

The behavior of the helical pitch in binary mixtures of cholesteric liquid crystals is studied by means of a simple molecular model (an extension to mixtures of a model introduced by Priest and Lubensky). The model exhibits helical inversion, and with some reasonable assumptions is shown to be capable of giving order of magnitude agreement with experiments performed by Baessler and Labes. It is found that helical inversion is driven by the variation with temperature of the nematic order parameters of the two components of the mixture. A general argument is given for the linearity of inverse pitch wavenumber versus concentration difference in the special case of a mixture of the left- and right-handed versions of a single cholesteric liquid crystal. (Such a system was studied experimentally by Dolphin et al.)